I haven't trained with too many over the years, but I think the phrase 'quality' over 'quantity' applies here.
Klay Pittman: Machado BB and badass competitor. Klay is very serious and dedicated to teaching BJJ, but recognizes that not every student is in the art for the sport. He has the ability to bring out the 'competitor' in every student no matter what their physical attributes are or aren't. He is extremely 'technical' in his instruction and takes lots of time to make sure you have the technique down and fully understand it. His game is amazing. I tapped to him about 6 times inside of 6 minutes!
Robert Defranco: Machado BB. Robert is lots of fun to train with! He has a very laid back attitude, but the training is awesome! Always open to questions and extremely thorough with the information he gives. But at times can be a bit harsh on my friend Marco! LOL
Raphael Lovato Sr: Machado BB. Mr Lovato is fantastic. Class is always a lot of fun and will get your cardio going fast! To be honest, I had heard lots of stories about him and not all were positive, but I like to find things out for myself. After meeting Lovato Jr, I was seriously impressed by his humble and open attitude, so I decided to give his academy a try. Mr Lovato is a highly dedicated teacher/trainer. He keeps the atmosphere relaxed enough that you can enjoy every minute of the class even when you are getting tapped out! I do that lot! LOL
Carlos Machado: What can I say that hasn't been said about the man. Simply Amazing! I personally don't think there is a better teacher of BJJ on the planet! Just look at the amazing track record of his students. Not to mention the fact that for about a decade Carlos was the "man to beat" in Brazil. The way I see it, Chuck Norris has enough money and pull to choose ANYBODY as a teacher to oversee his development in BJJ...but he chose Carlos!
Rigan Machado: One word...CRUSHING! I have never been squished that hard in my life! Rigan is also a lot of fun to train with and can get his point across pretty easily. I enjoyed the tremendous amount of detail he went into with every technique.
Although he doesn't teach his own class, forum member Rodney Poldrack does fill in for Robert Defranco quite a bit and will roll with and coach anybody that asks (except maybe Marco...). The times I have rolled with him, he was nice enough to just take it easy enough on me to make me work a bit before submitting me. When he finally does start his own school (hint hint) I am sure he will be very successful at it!
Finally, my first coach and close friend Jerry Smith, taught me from the ground up. I consider him to be the best training partner I have ever had. A humble guy but an absolute terror on the mat!